Bridges

For the design of rail viaducts in our congested cities and for rail viaducts having complex geometry with grade separation, the adoption of precast segmental construction techniques is becoming the almost universal approach. The transportation and erection of precast segments can be considered safer, easier to handle and more time efficient than similar activities with full span precast beams or by casting deck elements in situ. The design process is; however, challenging as each segment has to be detailed and cast to an accurate geometry taking account of the erection sequence, construction tolerance and the long-term effects including effects of shrinkage and creep.

The elevated rail viaduct of Jurong Region Line (JRL) is presently being designed and constructed in Singapore with deck sections formed entirely from precast segments. This paper looks in detail at Contract J102, the Design and Construction of Choa Chu Kang Station, Choa Chu Kang West Station, Tengah Station and the associated 4km of rail viaduct. It is one of the most challenging contracts, with viaduct on two levels, extended spans over highways of 90m in length and elsewhere tight radius curves. The design has been carried out using advanced analysis techniques such as parametric modelling, taking advantage of repetition to define segment dimensions adopting an automated process, which sets up the inputs for the BIM model.

The construction method has been adopted based on the bridge geometry, with some sections being as balanced cantilevers, and other sections opting for span-by-span erection techniques. In general, the deck is made integral with the piers over 4-5 spans, in an effort to eliminate bearings and reduce future maintenance. With it being a Design & Construct contract, the designer has worked closely with the contractor to optimise lifting weights, develop time efficient erection methods and programme key design and construction activities to meet a tight schedule.